High frequency magnetron apparatus



Patented May 24, 1932 UNITED STATES PATENT OFFICE ELMEB, D. MOLRTHUB, OISCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, ACORPORATION OF NEW YORK HIGH FREQUENCY MAGNETRON APPARATUS Applicationfiled August 28, 1929. Serial No. 389,067.

The present invention relates to the construction and operation ofelectron discharge apparatus and more particularly to devices in whichthe direction and flow of electrons are controlled by combined magneticand electrostatic fields in such a manner as to produce a negativeresistance characteristic, indicative of the ability to produceoscillations when connected in appropriate circuits.

Apparatus of this character employs a source of electrons and one ormore pairs of symmetrically arranged electron receiving surfaces, thetravel of electrons being directed by a suitably applied electrostaticfield and an externally located solenoid. .T he electron receivingsurfaces constitute anodes which usually take the form of segments of acylinder, While the source of electrons consists of a filament disposedin the longitudinal axis of the cylinder. A device of this sort may betermed, for convenience, a split anode magnetron and examples ofconstruction are disclosed and claimed in an application Serial No.285,008, filed in the name of K. Okahe, June 13, 1928, entitled Extrashort wave generating apparatus, also described by H. Yagi in an articleentitled Beam transmission of ultra short waves appearing in Proc. ofthe I. R. E. Vol. 16, June, 1928, pp. 735-6, and by K. Okabe in anarticle entitled On short wave limit of magnetron oscillations appearingin the Proc. of the I. R. E., Vol. 17, April 1929, pp. 652-659inclusive. It is stated in these disclosures that the split anodemagnetron offers an advantage over electrostatically controlled electrondischarge devices in that the interelectrode capacity is comparativelysmall and hence when the device is connected in suitable circuitsoscillations of short wave lengths and of considerable amplitude may begenerated.

It has been found in practice that while apparatus of this kind iscapable of producing oscillations of a much higher frequency than ispossible in a three-electrode grid controlled type of device, in view ofthe very small value of the interelectrode capacity referred tohereinbefore, there is still present suflicient capacity to preclude theproduction of oscillations of the shortest wave lengths useful in radiotransmission and reception e. g. of an order less than a few meters. Anobject of the present invention is to provide a magnetron of the splitanode type with an electrode construction which offers the minimumelectrostatic capacit This object is attained in brief, by providingrelatively flat anodes instead of cylindrical members and presentingeach anode edgewise, or substantially so, to the cathode.

It has been found further that the cylindrical form of anode in additionto failing to offer a minimum capacity also tends to heat unevenly overthe surface. The hottest portion of each anode resides in a restrictedregion along one axial edge while the remainder runs comparatively cooland it is apparent that the maximum output, deter mined by thetemperature of the hottest portion, is considerably lower than when theentire surface of the anode runs uniformly at the maximum elevatedtemperature. Accordingly, another object of the invention is to providean improved electrode construction and arrangement in which the anodemembers are heated evenly whereby the output may be maintained at anoptimum value.- I have discovered that a fiat anode construction lendsitself particularly well to this object under operating conditions aswell as to the previously stated object. Other objects and features ofthe invention will be apparent as the specification is perused inconnection with the accompanying drawings in which Fig. 1 is a sideelevational view of an impi;oved form of magnetron showing also a crosssection of the solenoid accessory and associated circuits; Fig. 2illustrates a crosssection of the device shown in Fig. 1 taken along theline 22; while Figs. 3 and 4 are graphs depicting certain operatingcharacteristics of the magnetron.

Referring to Fig. 1, numeral 1 designates a highly evacuated envelopecontaining a cathode in the form of a longitudinally dis-- posedrectilinear filament 2, supported at one end from the press 5 by meansof an anchor wire 6 and a tension spring 7. About the spring andattached to the upper filament May 24, 1932.

MILL/AMPS. HIV/f E. D. M ARTHUR HIGH FREQUENCY MAGNETRON APPARATUS FiledAug. 28, 1929 AMPERES HELD Inventor: Elmer D. TTIc Arthur,

His Attorney.

.- reference to a particular embodiment in which the anodes are locatedin a plane common to the filamentary cathode, it is evident that theadvantages .of my discovery also apply to those modifications in whichthe plane of the anodes does not contain the cathode or in which theanodes themselves do not lie in the same plane. From a purely efliciencystandpoint and apart from the interelectrode capacity or frequencyconsideration, the most effective position of the anodes Y may be suchthat the surface intercepts the path of electrons at an anglesubstantially normal thereto. The electron paths take the form ofspirals havin their origin at the cathode and the size of which isetermined by the instantaneous effect of the electrostatic and magneticfields. It is apparent so that as the electrodes are moved, ifnecessary,

out of line with one another, i.-e. sitioned in different planes, inorder to a apt their surfaces to the various electron'paths, theproJected area of each plate-like anode presented to the cathode or toone another becomes greater and the maximum frequenc of the generatedoscillations is correspon ingly reduced. However, it will be understoodthat notwithstanding the increased capacity under these conditlons, theflat form of anode offers a decided decrease in capacity effect over thecylindrical form. My mvention is therefore not limited to a uniplanararrangement of electrodes but contemplates all positions of the fiatanode in which advantage is taken to reduce inter-electrode capacity byreason of the anode configuration.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is 2- 1. In adevice for generating oscillations, an evacuatedenvelope containing a cathode, a plurality of anodes, means forproducing ed across the anodes, and a connection between the inductanceand the cathode.

3. In a device for generating oscillations, an evacuated envelopecontainin a cathode a plurality of anodes symmetrica y with respect tothe cathode, means for producing a cooperating magnetic field, a circuitcontaining a concentrated inductance and concentrated capacitanceconnected across the anodes, and a connection between said circuit andthe cathode, said anodes being constituted of plates arranged in a sin1e plane and resented edgewise to the cath e.

4 In a evice for generating oscillations, an evacuated envelopecontaining a rectilinear, filament, a plurality of substantially flatanodes presented edgewise to the filament, a solenoid disposed about theenvelope in such a manner t at the magnetic lines of force traverse thespace between the filament and the anodes in a direction parallelthereto, a resonant circuit connected between the anodes, a connectionbetween said circuit and the filament, said anodes being arranged in asingle plane common to the filament.

In wltness whereof, I have hereunto set my hand this 27 th day of A st,1929.

ELMER MoARTHUR.

a cooperating magnetic field, a resonant cir- I cuit connected acrossthe anodes and a connection between said circuit and the cathode, saidanodes being substantially flat and lying in the plane of the cathodewhereby the operating efliciency of the device is maintained at anoptimum value.

2. In a device for generating oscillations,

an evacuated envelope containing a cathode, a

4 plurality of substantiallyfiat anodes present,-

ed edgewise to the cathode, means for producing a cooperating magneticfield, a circuit containing inductance and capacitance connect-

